设计一个IIR滤波器，先设计模拟滤波器，再采用脉冲响应不变法和双线性变换法变换为数字滤波器-A IIR filter design, to design analog filter, then using constant impulse response and bilinear transform into a digital filter

用窗函数（矩形窗、汉宁窗、海明窗和布莱克曼窗）法设计FIR数字滤波器-Using the window function (rectangular window and hanning window, hamming window and blackman window) method to design FIR digital filter